Medium stacking device and image forming apparatus

ABSTRACT

A medium stacking device includes a medium stacking part stacking a medium, and a first movement part movably provided with respect to the medium stacking part. The first movement part has a first medium restriction part restricting a position of the medium, and a first movement restriction parts including a plurality of restriction members, each of which engaging with the medium stacking part and restricting a direction of the movement of the first movement part.

CROSS REFERENCE TO RELATED APPLICATION

The present application is related to, claims priority from andincorporates by reference Japanese Patent Application No. 2011-181664,filed on Aug. 23, 2011.

TECHNICAL FIELD

The present invention relates to an image forming apparatus, especiallyrelates to a configuration of a medium stacking device including a guidefor a medium to be stacked.

BACKGROUND

Conventionally, in such a medium stacking device, in order to regulate aposition of a sheet in a width direction which is orthogonal to acarrying direction of the stacked sheet, two sheet guides have beendisposed at the left and right of the sheet (see JP Laid-Open PatentApplication No. H8-034525 (page 3, FIG. 1).

However, since the conventional sheet guide cannot completely prevent anincline of the guided medium, the medium is sometimes inclined withrespect to the carrying direction. One of objects of the presentinvention is to eliminate the above mentioned problems by a simpleconfiguration.

SUMMARY

A medium stacking device of the present invention includes a mediumstacking part stacking a medium, and a first movement part movablyprovided with respect to the medium stacking part. The first movementpart has a first medium restriction part restricting a position of themedium, and a first movement restriction part including a plurality ofrestriction members, each of which engaging with the medium stackingpart and restricting a direction of the movement of the first movementpart.

According to the present invention, the first movement part can minimizethe incline of the medium which is being carried.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a main part configurationviewed from the front surface of an image forming apparatus of a firstembodiment employing a medium stacking device according to the presentinvention.

FIG. 2 is a configuration diagram viewed from the front surface (Y axisplus side) of a manual feed tray in the first embodiment.

FIG. 3 is an external perspective view illustrating the configuration ofthe medium stacking device in the first embodiment.

FIG. 4 is a configuration diagram viewed from the lower side of themedium stacking device in the first embodiment.

FIG. 5 is an external perspective view illustrating a configuration ofthe surface (upper surface) of a medium stacking plate of the mediumstacking device.

FIG. 6 is an external perspective view illustrating a configuration ofthe rear surface (lower surface) of the medium stacking plate.

FIG. 7 is an external perspective view illustrating a configuration of asheet guide illustrated in FIG. 3 in the first embodiment.

FIG. 8 is a diagram excluding the medium stacking plate from theconfiguration diagram of FIG. 4 in the first embodiment.

FIG. 9 is a K-K cross-sectional view illustrating a cross-section alonga position passing a center of screws illustrated in FIG. 4 in the firstembodiment.

FIG. 10 is a size explanation diagram illustrating a positionrelationship between the sheet guide installed to the medium stackingplate and a pinion gear rotatably axially fixed to the medium stackingplate in the first embodiment.

FIG. 11A is a partially enlarged diagram for explaining an engagementposition with a mesh of the pinion gear and a rack as an example in thefirst embodiment. FIG. 11B is a diagram illustrating another example ofa mesh of the pinion gear and the rack in the first embodiment.

FIG. 12 is a diagram used to an operation explanation of the sheet guideof the medium stacking device stacking recording sheets in the firstembodiment.

FIG. 13 is a configuration diagram viewed from the lower side of themedium stacking device in the second embodiment according to the presentinvention.

FIG. 14 is an M-M cross-sectional view illustrating a cross-sectionalong a position passing a center of screws shown in FIG. 13. The upperside of the medium stacking device is placed up.

FIG. 15 is a diagram used to an operation explanation of the sheet guideof the medium stacking device stacking recording sheets in the secondembodiment.

FIG. 16 is a configuration diagram of the medium stacking device viewedfrom the lower side in the third embodiment according to the presentinvention.

FIG. 17 is an external perspective view illustrating a configuration ofa sheet guide in the third embodiment.

FIG. 18 is an external perspective view illustrating a configuration ofa sheet guide in the fourth embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS First Embodiment

In FIG. 1, a sheet tray 51 is disposed, and a sheet feeding part 30 isprovided in a sheet feeding side of the sheet tray 51 in the lower partof an image forming apparatus 1 having a configuration as anelectrographic printer. Recording sheets 52 are stacked in the sheettray 51, and the sheet feeding part 30 feeds the recording sheets 52 asa media one by one. A pickup roller 31, a feed roller 32, and aseparation piece 33 are provided in the sheet feeding part 30. Thepickup roller 31 is provided so as to be contacted and pressed againstthe recording sheets 52 stacked to a certain height. The feed roller 32and the separation piece 33 separate the recording sheets 52 fed by thepickup roller 31 one by one.

A manual feed tray 300 is provided with a medium stacking device 302, apickup roller 303, a feed roller 304 and a retard roller 305. Therecording sheets 370 (FIG. 2) are stacked on the medium stacking device302. The pickup roller 303 is provided so as to be contacted and pressedagainst a contact part 311 (FIG. 2) of a medium stacking plate 310 ofthe medium stacking device 302. The feed roller 304 and the retardroller 305 separate the sheets one by one fed by the pickup roller 303.The recording sheets 370 on the medium stacking device 302 are fed tothe feed roller 304 by rotation of the pickup roller 303 by drive ofmotor (not shown), are separated one by one by the feed roller 304 andthe retard roller 305, and are sent to a sheet carrying part 40.

The sheet carrying part 40 carries each of the recording sheets 52 thatare separated into a sheet and fed from the sheet feeding part 30 to animage forming part 10 via carrying roller pairs 41, 42, and carries therecording sheets 370 (FIG. 2) separated into a sheet and fed from themanual feed tray 300 via the carrying roller pair 42 to the imageforming part 10 in the same manner. The image forming part 10 includesfour toner image forming parts 11K, 11Y, 11M, 11C (if not necessary tobe especially distinguished, may merely be referred to as a toner imageforming part 11) sequentially and tandemly arranged from the upstreamside of the carrying direction of the recording sheets 52, 370 and, atransfer part 13 transferring a toner image formed by the toner imageforming part 11 on the upper surface of the sheet by Coulomb force.

The toner image forming part 11K forms a black (K) toner image. Thetoner image forming part 11Y forms a yellow (Y) toner image. The tonerimage forming part 11M forms a magenta (M) toner image. The toner imageforming part 11C forms a cyan (C) toner image. In each toner imageforming part 11, the photosensitive drum 12 is charged by a chargingroller (not shown), image data is written on the rotating photosensitivedrum 12 by a light head (not shown), and the image data is developedwith toner. Thereby, each color of the toner images can be obtained onthe photosensitive drum 12.

The transfer part 13 includes a transfer belt 14 carrying the recordingsheet 52 carried from the sheet tray 51 or the recording sheet 370 (FIG.2) carried from the manual feed tray 300 in the arrow direction, andfour transfer rollers 15 disposed so as to face each photosensitive drum12 of each toner image forming part 11 across the transfer belt 14. Thetransfer part 13 sequentially transfers the toner image to the recordingsheet 52, the toner image for each color being formed by Coulomb forceon each photosensitive drum 12 corresponding to each toner image formingpart 11.

A fuser 20 fixes the toner image transferred on the recording sheets 52,370 in the transfer part 13 on the recording sheet by heat and pressure.The recording sheets 52, 370 on which the toner image is fixed areejected on a stacking part 56 on which the printed recording sheets arestacked via a carrying roller pair 53 and an ejection roller pair 54.

Each of the axes of X, Y, and Z, in FIG. 1 are as follows: X axis is thecarrying direction when the recording sheet 52 passes the image formingpart 10; Y axis is the rotation axial direction of the photosensitivedrum 12; and Z axis is the direction orthogonal to the above mentionedaxes. In addition, in a case where each of the axes of X, Y, and Z areshown in the other figures mentioned below, the rotation axialdirections respectively indicates identical directions. That is, X, Y,and Z axes in each of the figures show disposition directions ofdescription parts in each of figures configuring the image formingapparatus 1 shown in FIG. 1. Note that the image forming apparatus 1 isherein disposed so that Z axis is a substantially vertical direction.

FIG. 2 is a configuration diagram viewed from the front surface (Y axisplus side) of a manual feed tray 300. FIG. 3 is an external perspectiveview illustrating the configuration of the medium stacking device 302.FIG. 4 is a configuration diagram viewed from the lower side of themedium stacking device 302.

In FIG. 2, a frame 301 of the manual feed tray 300 is fixed to the imageforming apparatus 1 main body. The medium stacking device 302 stackingthe recording sheets 370 is rotatably held by the frame 301 as mentionedbelow. Note that parts other than the manual feed tray 300 of the imageforming apparatus 1 may referred to as the image forming apparatus 1main body. The pickup roller 303 is dispose at a position so as tocontact the contact part 311 of the medium stacking plate 310 of themedium stacking device 302. The feed roller 304 is rotatably held by theimage forming apparatus 1 main body, and is rotated and driven by adrive motor (not shown). An idler gear 306 links the pickup roller 304to the feed roller 303. The retard roller 305 is linked to a torquelimiter (not shown). A spring 308 biases the retard roller 305 towardthe feed roller 304. A spring 309 biases the medium stacking device 302toward a direction in which the contact part 311 of the medium stackingdevice 302 contact pickup roller 303.

Note that the manual feed tray 300 herein, for example, includes theframe 301, the medium stacking device 302, the pickup roller 303, thespring 309, and the idler gear 306.

As shown in FIG. 3 and FIG. 4, the medium stacking device 302 includesthe medium stacking plate 310 as a medium stacking part, a sheet guide320 as a first movement part, a sheet guide 321 as a second movementpart, a pinion gear 381 as a first gear part, and a pinion gear 382 as asecond gear part. A pair of posts 335, 336 formed on both of end partsof the medium stacking plate 310 are respectively inserted into guidegrooves 301 a, 301 b (FIG. 2) formed on the frame 301. Thereby, themedium stacking device 302 is rotatably held. Furthermore, as mentionedabove, the contact part 311 of the medium stacking device 302 is biasedin the direction where the contact part 311 contacts the pickup roller303 by the spring 309. The pinion gears 381 and 382 are positioned alongin the medium carrying direction and at a substantially middle of thesheet guides 320 and 321.

FIG. 5 is an external perspective view illustrating a configuration ofthe surface (upper surface) of a medium stacking plate 310 of the mediumstacking device 302. FIG. 6 is an external perspective view illustratinga configuration of the rear surface (lower surface) of the mediumstacking plate 310.

As shown in FIG. 5 and FIG. 6, a center plate part 340 is formed in acenter part of the medium stacking plate 310, and extends in a directionof arrow A (vertical to Y axis, however not always vertical to Z axis)indicating a carrying direction of the stacked recording sheets 370(FIG. 2). Guide grooves 331, 332, 333, 334 are alternately formed fromboth sides of the center plate part 340. The guide grooves extend in awidth direction (Y axis direction) of the stacked recording sheets. Aninsertion part 331 a, 332 a, 333 a, 334 a is formed in each guide groove331-334. The insertion parts 331 extend outward only a predeterminedwidth in both directions which are orthogonal each other in a positionclose to the center plate part 340. All of the guide grooves 331-334 andthe insertion parts 331 a-334 a penetrate to the rear side of the mediumstacking plate 310 as shown in FIG. 6.

FIG. 7 is an external perspective view illustrating a configuration of asheet guide 320 illustrated in FIG. 3. Note that since the configurationof the sheet guide 321 herein is identical to that of the sheet guide320, the configuration will be explained with reference to the sheetguide 320.

The sheet guide 320 includes a guide block 350 extending in thedirection of arrow A along which the stacked recording sheets arecarried, and a pair of racks 355, 356 as a first movement restrictionpart extending in the width direction (Y axis direction) of therecording sheet. A restriction surface 351 as a first medium restrictionpart and a stacking surface 352 a are formed in the guide block 350. Therestriction surface 351 that is vertical surface with respect to Y axis,extends in the direction of arrow A, and restricts a position of thewidth direction of the recording sheet. The stacking surface 352 a thatis orthogonal to the restriction surface 351 extends in the direction ofarrow A. The edges of the width direction of the recording sheets arestacked on the stacking surface 352 a. Note that a pair of racks 355,356 of the sheet guide 321 corresponds to a second movement restrictionpart. The restriction surface 351 of the sheet guide 321 corresponds toa second medium restriction part. In this embodiment, each of themovement restriction parts is realized with two restriction members(racks 355 and 356). The number of the restriction members for onemovement restriction part is preferably two, but may be three or more.

Rack holding members 353, 354 respectively holding the racks 355, 356are formed below a plate-shaped part 352. The upper surface of theplate-shaped part 352 is the stacking surface 352 a. The each rack 355,356 projects downward from the lower surface of the plate-shaped part352 so that the upper surface of each rack 355, 356 and the lowersurface of the plate-shaped part 352 have a predetermined interval g. Asshown in FIG. 7, the racks 355, 356 have the predetermined intervalbetween them, and are formed at a position where the racks shifted inthe direction of arrow A with respect to a width center of the guideblock 350. The position relationship of these will be explained below.

The rack 355 and the rack 356 are plate-shaped members having flatsurfaces in parallel to the stacking surface 352 a. The racks 355 andthe rack 356 are formed vertically with respect to the restrictionsurface 351, and have a substantially identical shape, and are formed inparallel. A restriction part 355 b and a restriction part 356 b areformed in one edge of the guide block side of the rack 355 and the rack356. A restriction part 355 f and a restriction part 356 f are formed inthe other edge of the guide block side of the rack 355 and the rack 356.In addition, in the opposite side of arrow A of the rack 355 and therack 356, a tooth part 355 d and a tooth part 356 d are formed betweenboth of the restriction parts, and in the arrow A side, a pair of biasparts 355 c, 355 e and a pair of bias parts 356 c, 356 e are formed inthe neighborhood of both of the restriction parts.

As shown in FIG. 3 and FIG. 4, the rack holding members 353, 354 of thesheet guide 320 are installed to the medium stacking plate 310 so thatthe rack holding members 353, 354 are respectively guided to the guidegrooves 333, 331 of the medium stacking plate 310. The rack holdingmembers 353, 354 of the sheet guide 321 are installed to the mediumstacking plate 310 so that the rack holding members 353, 354 arerespectively guided to the guide grooves 332, 334 of the medium stackingplate 310. Installation method of the guide grooves will be explainedhereinafter.

Here, the case where the sheet guide 320 shown in FIG. 7 is installed tothe medium stacking plate 310 shown in FIG. 5 and FIG. 6 will beexplained. First, the sheet guide 320 is rotated substantially 90degrees around X axis in a direction of arrow B. Respectively, a frontedge of the restriction part 355 f of the rack 355 is inserted in adirection of arrow C (FIG. 5) so that the front edge is substantiallyvertically inserted into the insertion part 333 a of the guide groove333 of the medium stacking plate 310. In addition, a front edge of therestriction part 356 f of the rack 356 is inserted in a direction ofarrow C (FIG. 5) so that the front edge is substantially verticallyinserted into the insertion part 331 a of the guide groove 331 of themedium stacking plate 310. The sheet guide 320 is pushed and entereduntil the plate-shaped part 352 abuts on the upper surface of the mediumstacking plate 310.

For this reason, the width of the insertion part 333 a is made to bewider than each width Wa1, Wa2 of the restriction parts 355 b, 355 f. Inaddition, the width of the insertion part 333 a is made to be wider thaneach width Wb1, Wb2 of the restriction parts 356 b, 356 f. Furthermore,the width of the rack holding part 353 is made to be narrower than eachwidth Wa1, Wa2 of the restriction parts 355 b, 355 f. The width of theguide groove 333 is formed to have a width suitable for guiding theinserted rack holding member 353. In the same manner, the width of therack holding part 354 is made to be narrower than each width Wb1, Wb2 ofthe restriction parts 356 b, 356 f. The width of the guide groove 331 isformed to have a width suitable for guiding the inserted rack holdingmember 354.

At the stage where the plate-shaped part 352 abuts on the upper surfaceof the medium stacking plate 310, the sheet guide 320 is rotated aroundX axis in the opposite direction of a direction of arrow B . Thereby,the rack holding member 353 and the rack holding member 354 isrespectively inserted into to the guide groove 333 and the guide groove331, and the rack 355 and the rack 356 respectively extends in parallelvia the medium stacking plate 310 on the lower surface of the mediumstacking plate 310. Furthermore, until the guide block 350 is positionedat one end side of the medium stacking plate 310, the sheet guide 320 isguided and moved by the guide grooves 333, 331. Thereby, the sheet guide320, for example, as shown in FIG. 3, is placed at an initial position.The initial position mentioned herein indicates a farthest part positionof the sheet guide 321.

In the same manner, a front edge of the restriction part 355 f of therack 355 of the sheet guide 321 is inserted in a direction of arrow C(FIG. 5) so that the front edge is substantially vertically insertedinto the insertion part 332 a of the guide groove 332 of the mediumstacking plate 310. In addition, a front edge of the restriction part356 f of the rack 356 is inserted in a direction of arrow C (FIG. 5) sothat the front edge is substantially vertically inserted into theinsertion part 334 a of the guide groove 334 of the medium stackingplate 310. Until the guide block 350 is positioned at another end sideof the medium stacking plate 310, the sheet guide 321 is guided andmoved by the guide grooves 332, 334. Thereby, the sheet guide 321, forexample, as shown in FIG. 3, is placed at the initial position.

As shown in FIG. 4 and FIG. 6, the guide wall 341 a and the guide wall341 b are formed on the lower surface of the medium stacking plate 310.The guide wall 341 a faces the bias parts 356 c, 356 e of the rack 356of the sheet guide 320. The guide wall 341 b faces the abutment parts356 a, 356 g of the rack 356 of the sheet guide 320. The abutment parts356 a, 356 g receive bias force from the bias parts 356 c, 356 e,contact the guide wall 341 b, and guide the movement of the rack 356 ofthe sheet guide 320 without shaking the sheet guide. In the same manner,the guide wall 342 a and the guide wall 342 b are formed on the lowersurface of the medium stacking plate 310. The guide wall 342 a faces thebias parts 355 c, 355 e of the rack 355 of the sheet guide 320. Theguide wall 342 b faces the abutment parts 355 a, 355 g of the rack 355of the sheet guide 320. The abutment parts 355 a, 355 g receive biasforce from the bias parts 355 c, 355 e, contact the guide wall 342 b,and guide the movement of the rack 355 of the sheet guide 320 withoutshaking the sheet guide. The guide walls 341 a and 341 b functions assupport parts for the abutment parts 356 a and 356 g. The support partsfunction to allow the first and second medium restriction parts to movein predetermined directions. In the embodiments, the abutment parts 355a, 355 g of the rack 355 contact the guide walls 341 a, 341 b, andslidably move along the surfaces of the guide walls 341 a, 34 lb. Aslong as the support parts allows the medium restriction parts to movewithout shaking the sheet guide, there is no structural or materialrestriction for the support parts. For example, the support part mayhave a curved surface other than the plane surface. The support part mayhave a projection shape which protrudes toward the abutment part and ofwhich a tip contacts the abutment part so that the movement of theabutment part is restricted by the tip of the support part.

In the same manner, the guide wall 344 a and the guide wall 344 b areformed on the lower surface of the medium stacking plate 310. The guidewall 344 a faces the bias parts 356 c, 356 e of the rack 356 of thesheet guide 321. The guide wall 344 b faces the abutment parts 356 a,356 g of the rack 356 of the sheet guide 321. The abutment parts 356 a,356 g receive bias force from the bias parts 356 c, 356 e, contact theguide wall 344 b, and guide the movement of the rack 356 of the sheetguide 321 without shaking the sheet guide. In the same manner, the guidewall 343 a and the guide wall 343 b are formed on the lower surface ofthe medium stacking plate 310. The guide wall 343 a faces the bias parts355 c, 355 e of the rack 355 of the sheet guide 321. The guide wall 343b faces the abutment parts 355 a, 355 g of the rack 355 of the sheetguide 321. The abutment parts 355 a, 355 g receive bias force from thebias parts 355 c, 355 e, contact the guide wall 343 b, and guide themovement of the rack 355 of the sheet guide 321 without shaking thesheet guide.

FIG. 8 is a diagram excluding the medium stacking plate 310 from theconfiguration diagram of FIG. 4 in the first embodiment. FIG. 9 is a K-Kcross-sectional view illustrating a cross-section along a positionpassing a center of screws 345, 346 illustrated in FIG. 4.

As shown in FIG. 8, the sheet guide 320 and the sheet guide 321 have asubstantially identical shape. When the sheet guides are installed tothe medium stacking plate 310 and each the sheet guide is at the initialposition, in the direction of arrow A that is the moving direction ofthe recording sheet, the racks 355, 356 of each sheet guide alternatelyare disposed in parallel at a predetermined interval. Especially, thetooth part 355 d of the sheet guide 320 is adjacent to the tooth part356 d of the sheet guide 321 and the tooth part 356 d of the sheet guide320 is adjacent to the tooth part 355 d of the sheet guide 321. One partof a region of each of front edge sides of the tooth parts adjacent toeach other face at a predetermined interval in the center part of thewidth direction (Y axis direction) of the recording sheet 370 of themedium stacking plate 310.

As shown in FIG. 8, the pinion gear 381 and the pinion gear 382 arerespectively disposed in the center part of the width direction of therecording sheet 370 of the medium stacking plate 310 at a position wherethe tooth part 356 d of the sheet guide 320 and the tooth part 355 d ofthe sheet guide 321 face, and a position where the tooth part 355 d ofthe sheet guide 320 and the tooth part 356 d of the sheet guide 321face. The pinion gear 381 and the pinion gear 382 are respectivelyrotatably fixed at the medium stacking plate 310 by the screw 345 andthe screw 346.

As shown in FIG. 9, the tooth part 381 a and a flange part 381 b areformed in the pinion gear 381. The tooth part 381 a meshes with thetooth part 356 d of the rack 356 of the sheet guide 320 and with thetooth part 355 d of the rack 355 of the sheet guide 321. The flange part381 b projects so as to cover each part of the rack 356 of the sheetguide 320 and the rack 355 of the sheet guide 321. In the same manner,the tooth part 382 a and a flange part 382 b are formed in the piniongear 382. The tooth part 382 a meshes with the tooth part 356 d of therack 356 of the sheet guide 321 and with the tooth part 355 d of therack 355 of the sheet guide 320. The flange part 382 b projects so as tocover each part of the rack 356 of the sheet guide 321 and the rack 355of the sheet guide 320. Note that, in FIGS. 4, 8, only each pitch circle(standard circle) 381 p, 382 p of each tooth part 381 a, 382 a of thepinion gear 381, 382 are shown by dotted lines.

The plate-shaped part 352 of the guide block 350 of the sheet guide 320installed to the medium stacking plate 310 is restricted by the mediumstacking plate 310. In addition, the racks 355, 356 of the sheet guide320 are restricted by each of the flange parts 381 b, 382 b of thepinion gears 381, 382. Accordingly, the sheet guide 320 is not detachedbelow (here, the minus side of Z axis). In addition, since the widths ofthe racks 355, 356 are respectively formed wider than the widths of theguide grooves 331, 333 of the medium stacking plate 310. Accordingly,the sheet guide 320 is not detached above (here, plus side of Z axis).In the same manner, the sheet guide 321 installed to the medium stackingplate 310 is configured so as not to detach in upper and lowerdirections with respect to the medium stacking plate 310.

Note that, as shown in FIG. 9, a wave washer 383 is arranged in acompressed manner between the pinion gear 382 and the medium stackingplate 310, and biases the pinion gear 382 toward the screw 346. Thiswave washer 383 adjusts a rotation load of the pinion gear 382, andthereby, adjusts the movement load of the sheet guides 320, 321. Thewave washer 383 may respectively be provided to the two pinion gears381, 382. However, here, as described below since two of the piniongears 381 and 382 link each other, the wave washer 383 may provided onlyto the pinion gear 382.

As shown in FIG. 4 (see FIG. 8), the abutment parts 356 a, 356 g of thesheet guide 320 contact the guide wall 341 b of the medium stackingplate 310 by bias from the bias parts 356 c, 356 e, and restrict an meshposition of the pinion gear 381 and the rack 356 as well as a movementrange of the sheet guide 320 with respect to the medium stacking plate310. In the same manner, the abutment parts 355 a, 355 g of the sheetguide 320 contact the guide wall 342 b of the medium stacking plate 310by bias from the bias parts 355 c, 355 e, and restrict an mesh positionof the pinion gear 382 and the rack 355 as well as a movement range ofthe sheet guide 320 against the medium stacking plate 310.

Meanwhile, the abutment parts 356 a, 356 g of the sheet guide 321contact the guide wall 344 b of the medium stacking plate 310 by biasfrom the bias parts 356 c, 356 e, and restrict an mesh position of thepinion gear 382 and the rack 356 as well as a movement range of thesheet guide 321 with respect to the medium stacking plate 310. In thesame manner, the abutment parts 355 a, 355 g of the sheet guide 321contact the guide wall 343 b of the medium stacking plate 310 by biasfrom the bias parts 355 c, 355 e, and restrict an mesh position of thepinion gear 381 and the rack 355 as well as a movement range of thesheet guide 321 against the medium stacking plate 310.

FIG. 10 is a size explanation diagram illustrating a positionrelationship between the sheet guides 320, 321 installed to the mediumstacking plate 310 and the pinion gears 381, 382 rotatably axially fixedto the medium stacking plate 310. Note that, here, for the sake ofconvenience, “′” are putted to the reference numbers of eachconfiguration element of the sheet guide 321, to distinguish eachconfiguration element of the sheet guide 320. Note that FIG. 10corresponds to FIG. 8 the medium stacking device 302 viewed from thelower side (the minus side of Z axis), and the direction of arrow A inFIG. 10 shows the carrying direction of the stacked recording sheet.

As shown in the above figure, the sheet guides 320, 321 have the sameidentical figure. Restriction surfaces 351, 351′ face each other andextend in the direction of arrow A. And the racks 355, 356 of the sheetguide 320 and the racks 355′, 356′ of the sheet guide 321 are disposedso as to be alternately positioned in the direction of arrow A.Furthermore, the pinion gear 381 is disposed so as to mesh with each ofthe racks between the rack 356 of the sheet guide 320 and the rack 355′of the sheet guide 321 extending each other in parallel. The pinion gear382 is disposed so as to mesh with each of the racks between the rack355 of the sheet guide 320 and the rack 356′ of the sheet guide 321.

A length in the direction of arrow A of the guide block 350 (350′) isdefined as L. A diameter of each pitch circle (standard circle) 381 p,382 p of each pinion gear 381, 382 disposed in line in direction ofarrow A is defined as d. A position relationship between the rack 355(355′) and the rack 356 (356′) extending in parallel to the rack 355will be explained.

A hypothetical center line being the perpendicular bisector between eachof rotation centers 381 c, 382 c of the pinion gears 381, 382 andextending in a width direction (Y axis direction) of the stackedrecording sheet is defined as P. A distance from the hypothetical centerline P to the rotation center 381 c is defined as X. A distance from thehypothetical center line P to the rotation center 382 c is defined as X.

At this time, a distance from the hypothetical center line P to a pitchline (standard line) 355 p′ of the rack 355′ being an engagementposition of the pinion gear 381 is defined as Z. The distance Z isobtained by the following Formula:

Z=X−d/2.

The tooth part 355 d (FIG. 8) is formed so that this position is a pitchline (standard line) 355 p′ of the rack 355′. In addition, a distancefrom the pitch line (standard line) 355 p′ of the rack 355′ to a pitchline (standard line) 356 p′ of the rack 356′ being the engagementposition with the pinion gear 382 is defined as Y. The distance Y isobtained by the following Formula:

Y=2X.

The tooth part 356 d (FIG. 8) is formed so that this position is a pitchline (standard line) 356 p′ of the rack 356′.

In addition, with respect to the restriction surface 351′ having thelength L in the direction of arrow A, the substantially center in thedirection of arrow A of the restriction surface 351′ is disposed so asto coincide with the hypothetical central line P, and at least one ofthe racks 355′, 356′ is disposed in the direction of arrow A side(downstream side) and the opposite side of the direction of arrow A side(upstream side) based on the substantially center. Note that, in thedrawing, rack 355′ on the downstream side, rack 356′ on the upstreamside. In this case, obviously shown in the arrangement in FIG. 10, whena width of the rack 355′ is defined as w1, and a width of the rack 356′is defined as w2, Z and K are necessary to be set by the followingformulae:

Z>w1, and

K=L/2−(Z+d)>w2.

By forming in this manner, the sheet guide 320 and the sheet guide 321having the same shape can be disposed and face each other, can beinstalled to the medium stacking plate 310.

Note that, here, the substantially center in the direction of arrow A ofthe restriction surface 351′ is disposed so as to coincide with thehypothetical central line P. However, if the substantially centermentioned herein indicates the hypothetical center line P being includedin a region having a length of L/2±20%, same effects can be obtained bythe arrangement of the line P.

In addition, the engagement position mentioned herein is a positionwhere the pinion gear 381 meshes with the racks 355′, 356, and thepinion gear 382 meshes with the racks 355, 356′. FIGS. 11A and 11B arepartially enlarged diagrams for explaining an engagement position with amesh of the pinion gear 381 and the rack 355′ as an example.

As shown in FIG. 11A, the pinion gear 381 and the rack 355′ are engagedso that one of tangential lines of the pitch circle (standard circle)381 p of the pinion gear 381 is positioned in the substantially centerof a range h2 from an addendum to a dedendum of the tooth part 355 d′ ofthe rack 355′. A position on the rack 355′ where the pitch circle(standard circle) 381 p of the pinion gear 381 contacts in this waycorresponds to the pitch line (standard line) 355 p′ of the rack.Accordingly, the engagement position mentioned herein corresponds to aposition where the pitch circle (standard circle) of the pinion gearcontacts the pitch line (standard line) of the rack.

The above mentioned engagement position is merely one example. Theengagement position may be a position in a region where a range h1 andthe range h2 intersect. The range h1 is from the addendum to thededendum of the tooth part 381 a of the pinion gear 381. The range h2 isfrom the addendum to the dedendum of the tooth part 355 d′ of the rack355′. For example, as shown in FIG. 11B, in a case where the pinion gear381 is shifted, a position relationship causing the pinion gear 325 toengage with the rack 355′ differs from that shown in FIG. 11A. Theengagement position of the other pinion gear with the rack is identicalto the above mentioned engagement position.

In addition, for example, the tooth part 355 d of the rack 355 and thetooth part 356 d of the rack 356 have the identical pitch and theidentical phase viewed from the restriction surface 351 in the sheetguide 320 shown in FIG. 7. The sheet guide 321 is configured in the samemanner as mentioned above. In addition, for example, the pinion gear 381and the pinion gear 382 shown in FIG. 8, have the identical number ofteeth, and as shown in FIG. 11, the number herein is 16, which is evennumber. Furthermore, the pinion gears respectively include the flangeparts 381 b, 382 b, and have the identical module.

In the above mentioned configuration, operation of the sheet guides 320,321 in the medium stacking device 302 of the manual feed tray 300 willbe explained with reference to FIG. 12. Note that FIG. 12 is a diagramused to an operation explanation of the sheet guides 320, 321 of themedium stacking device 302 stacking recording sheets 370. In the abovefigure, only a region in the recording sheet 370 where the mediumstacking device exists is specified by drawing with diagonal lines.

Firstly, the medium stacking device 302 is pushed down against bias ofthe spring 309 by an operation device (not shown), so that the contactpart 311 of the medium stacking device 302 shown in FIG. 2 is separatedonly at a predetermined interval from the pickup roller 303, and themedium stacking device 302 is restricted at the position where themedium stacking device 302 is pushed down. In the state where the mediumstacking device 302 is pushed down in this way, the recording sheets 370are placed on the manual feed tray 300. At this time, the sheet guide320 and the sheet guide 321 are moved to outside and the recordingsheets 370 are stacked on the medium stacking device 302 so that thewidth direction edges of the recording sheet 370 are positioned on eachof the stacking surfaces 352 a of the sheet guide 320 and the sheetguide 321. Each of the restriction surfaces 351 of the sheet guides 320and 321 are moved in a center direction until the restriction surfaces351 abut on end surfaces of the recording sheets 370.

At this time, each of the restriction surfaces 351 of the sheet guide320 and the sheet guide 321 are symmetrically moved away from and towarda line connecting each of the rotate center s of the pinion gears 381and 382 (see FIG. 8) as the center line. Accordingly, when the guideblock 350 of either the sheet guide 320 or sheet guide 321 is moved, theother guide block 350 is also symmetrically moved via the pinion gears.Thereby, the width direction position of the recording sheet 370 can berestricted.

As mentioned above, since the tooth part 355 d of the rack 355 and thetooth part 356 d of the rack 356 are configured to have the identicalpitch and the identical phase viewed from the restriction surface 351,and the pinion gear 381 and the pinion gear 382 have the identicalshape, even if a rack and pinion is configured with the two racks 355,356 in this way, sliding motion can be smoothly performed.

After determination of a position of the width direction of therecording sheet 370 on the medium stacking device 302 is performed asmentioned above, position restriction by an operation device (not shown)is unlocked, and as shown in FIG. 2, the top sheet of the stackedrecording sheets 370 contacts the pickup roller 303 by bias force of thespring 309. In such a state, the pickup roller 303 activates and therecording sheet 370 is fed, the recording sheet 370 is fed in thedirection of arrow A in FIG. 12. At this time, the recording sheet 370may skew in a rotation direction of either arrow Ma or arrow Mb.

For example, when the recording sheet 370 skews in the direction ofarrow Ma, the rear edge side in the direction of arrow A of therestriction surface 351 of the sheet guide 321 receives a pressure forceFa from the recording sheet 370 generated by skew, and the front edgeside in the direction of arrow A of the restriction surface 351 of thesheet guide 320 receives a pressure force Fc from the recording sheet370 generated by skew. At this time, a movement force Fd is generated atthe front edge side of the sheet guide 321 toward the center directionto rotate in the direction of arrow Mc, a movement force Fb is generatedat the rear edge side of the sheet guide 320 toward the center directionto rotate in the direction of arrow Md.

At this time, the movement force Fd, which is generated at the frontedge side of the sheet guide 321, is led to the front edge side of thesheet guide 320 via the rack 355′ of the sheet guide 321, the piniongear 381, the rack 356 of the sheet guide 320 shown in FIG. 10, andreaches the front edge side of the sheet guide 320 as a force cancellingthe pressure force Fc from the recording sheet 370. In the same manner,the movement force Fb, which is generated at the rear edge side of thesheet guide 320, is led to the rear edge side of the sheet guide 321 viathe rack 355 of the sheet guide 320, the pinion gear 382, the rack 356′of the sheet guide 321 shown in FIG. 10, and reaches the rear edge sideof the sheet guide 320 as a force cancelling the pressure force Fa fromthe recording sheet 370.

In a case where the recording sheet 370 skews in the direction of arrowMb, in the same manner, a pressure force which each sheet guide 320, 321respectively receives from the recording sheet 370 is cancelled.

As mentioned above, according to the medium stacking device of theembodiment, since the pinion gears 381, 382 arranged at the positionsbeing separated in the direction of arrow A respectively link to theracks extending from the sheet guides 320, 321, even if skew isgenerated in the carried recording sheet, an incline of the sheet guides320, 321 is suppressed, and the skew of the recording sheet can bediminished.

Second Embodiment

FIG. 13 is a configuration diagram viewed from the lower side (the minusside of Z axis) of the medium stacking device 402 in the secondembodiment according to the present invention. FIG. 14 is an M-Mcross-sectional view illustrating a cross-section along a positionpassing a center of screws 345, 346 shown in FIG. 13. The upper side ofthe medium stacking device 402 is placed up in FIG. 4.

The image forming apparatus employing this medium stacking device 402has main different points from the image forming apparatus employing theabove mentioned medium stacking device 302 of the first embodiment shownin FIG. 4. The points are that, for example, upper layer gears 481 d,482 d are added to the pinion gears 481, 482 (381, 382 in embodiment 1)and the pinion gears are formed as a two stage gear, and that an idlergear 400 meshing with these upper gears 481 d, 482 d is added. In theinvention, a transferring part means a part that functions to convey apower from the first gear part to the second gear part. In thisembodiment, the transferring part is configured with the upper layergears 481 d, 482 d and idler gear 400. As long as the transferring partis able to convey the power from the first gear part to the second gearpart, there is no structural restriction. The number of parts, gears forthe transferring part vary according to the configuration. Instead ofthe mechanical structure by gears discussed above, friction force ormagnetic force may be useful to realized the transferring part.

Accordingly, the same reference numbers are put to, and explanation andfigures are omitted for parts of the image forming apparatus employingthis medium stacking device 402 that are common with the image formingapparatus 1 of the first embodiment mentioned above (FIG. 1). Differentparts of the image forming apparatus from those of the image formingapparatus 1 are intensively explained. Note that since the mainconfiguration of the image forming apparatus of the embodiment is commonwith the main configuration of the image forming apparatus 1 of thefirst embodiment shown in FIG. 1 other than the medium stacking device402, FIGS. 1, 2 will be referred if needed.

In FIG. 13 and FIG. 14, in the pinion gears 481, 482, not only the firststage gear meshing with each rack, as explained in the first embodiment,but also the upper layer gears 481 d, 482 d being a second stage gearare formed via flange parts 481 b, 482 b. In FIG. 13, pitch circles ofthe upper layer gears 481 d, 482 d are shown. The idler gear 400 isdisposed in the center part of these pinion gears 481,482, and isrotatably fixed in the center point between axes of the pinion gears481, 482 by a screw 401 to medium stacking plate 310. In FIG. 13, apitch circle 400 p of the idler gear 400 is shown by dotted lines.

As shown in FIG. 14, a wave washer 405 is arranged in a compressedmanner between the idler gear 400 and the medium stacking plate 310 and,biases the idler gear 400 toward the screw 401. Note that a notch part455 h for allowing attachment of the idler gear 400 to the mediumstacking plate 310 is formed in a rack 455 (355 in the first embodiment)of the sheet guides 420, 421 (320, 321 the first embodiment).

The idler gear 400 respectively meshes with each upper layer gear 481 d,482 d of these pinion gears 481, 482 at the center parts of the piniongears 481, 482 and causes the pinion gear 481 to link to the pinion gear482.

Note that, here, the sheet guide 420 corresponds to a first movementpart. The sheet guide 421 corresponds to a second movement part. Thepair of racks 455, 456 of the sheet guide 420 corresponds to a firstmovement restriction part. The pair of racks 455, 456 of the sheet guide421 corresponds to a second movement restriction part. The restrictionsurface 351 of the sheet guide 420 corresponds to a first mediumrestriction part. The restriction surface 351 of the sheet guide 421corresponds to a second medium restriction part.

In the above mentioned configuration, operation of the sheet guide 420,421 in the medium stacking device 402 of will be explained withreference to FIG. 15. Note that FIG. 15 is a diagram used to anoperation explanation of the sheet guides 420,421 of the medium stackingdevice 402 stacking the recording sheets 370. In the above figure, onlya region in the recording sheet 370 where the medium stacking deviceexists is specified by drawing with diagonal lines.

Firstly, the medium stacking device 402 is pushed down against bias ofthe spring 309 by an operation device (not shown), so that the contactpart 311 of the medium stacking device 302 shown in FIG. 2 (hereinreferred to as 402) is separated only at a predetermined interval fromthe pickup roller 303, and the medium stacking device 402 is restrictedat the position where the medium stacking device 402 is pushed down. Inthe state where the medium stacking device 402 is pushed down in thisway, the recording sheets 370 are placed on the manual feed tray 300. Atthis time, the sheet guide 420 and the sheet guide 421 are moved tooutside and the recording sheets 370 are stacked on the medium stackingdevice 402 so that the width direction edges of the recording sheet 370are positioned on each of the stacking surfaces 352 a of the sheet guide420 and the sheet guide 421. Each of the restriction surfaces 351 of thesheet guides 420 and 421 are moved in a center direction until therestriction surfaces 351 abut on end surfaces of the recording sheets370.

At this time, each of the restriction surfaces 351 of the sheet guide420 and the sheet guide 421 are symmetrically moved away from and towardand a line connecting each of the rotate centers of the pinion gears 481and 482 (see FIG. 13) as the center line. At this time, the pinion gear481 and the pinion gear 482 simultaneously rotate in the identicaldirection with the movement of the sheet guide 420 and the sheet guide421, while the idler gear 400 links these gears rotating in the oppositedirection. As mentioned above, in the case where the idler gear 400 isadded, even the two racks 455,456 are used to configure the rack andpinion, sliding motion can be smoothly performed.

Thereby, after determination of a position of the width direction of therecording sheet 370 on the medium stacking device 402 is performed asmentioned above, position restriction by an operation device (not shown)is unlocked and as shown in FIG. 2, the top sheet of the stackedrecording sheets 370 contacts the pickup roller 303 by bias force of thespring 309. In such a state, the pickup roller 303 activates and therecording sheet 370 is fed, the recording sheet 370 is fed in thedirection of arrow A in FIG. 15. At this time, the recording sheet 370may skew in a rotation direction of either arrow Ma or arrow Mb.

For example, when the recording sheet 370 skews in the direction ofarrow Ma, the rear edge side in the direction of arrow A of therestriction surface 351 of the sheet guide 421 receives the pressureforce Fa from the recording sheet 370 generated by skew. At this time,the front edge side of the sheet guide 420 generates the movement forceFd toward the center direction to rotate in the direction of arrow Mc.

These forces generated by skew toward the direction of arrow Ma causethe pinion gear 481 and the pinion gear 482 (FIG. 13) to rotate in theopposite direction each other. However, these pinion gear 481 and piniongear 482 linked by the idler gear 400 cannot rotate in the oppositedirection each other. Accordingly, the sheet guide 421 does not rotatein the direction of arrow Ma. In the same manner, in a case where therecording sheet 370 skews toward the direction of arrow Mb, the sheetguide 421 does not rotate in direction of arrow Mb. Since the forces actwith respect to the sheet guide 420 in the same manner, the sheet guide420 and the sheet guide 421 can always keep the respective restrictionsurfaces 351 in parallel with respect to the direction of arrow A beingthe sheet carrying direction.

As mentioned above, according to the medium stacking device of theembodiment, since the pinion gears 481, 482 arranged at the positionsbeing separated in the direction of arrow A link to the idler gear 400,even if skew is generated in the carried recording sheet, thereby, sincean incline of the sheet guides 420, 421 is suppressed, and the skew ofthe recording sheet can be diminished.

Third Embodiment

FIG. 16 is a configuration diagram of the medium stacking device 502viewed from the lower side (the minus side of Z axis) in the thirdembodiment according to the present invention. FIG. 17 is an externalperspective view illustrating a configuration of a sheet guide 520(521).

The image forming apparatus employing this medium stacking device 502has a main different point from the image forming apparatus employingthe above mentioned medium stacking device 302 of the first embodimentshown in FIG. 4. The point is that instead of the pinion gears 381, 382,the flanges 581, 582 without a gear are fixed by the screws 345, 346 tothe medium stacking plate 310, and plate-shaped extending parts 555, 556are formed instead of the racks in each sheet guide 520, 521. In thisembodiment, the movement restriction parts are realized with tworestriction members (extending parts 555 and 556). The number of therestriction members for one movement restriction part is preferably two,but may be three or more.

Accordingly, the same reference numbers are put to, and explanation andfigures are omitted for parts of the image forming apparatus employingthis medium stacking device 502 that are common with the image formingapparatus 1 of the first embodiment mentioned above (FIG. 1). Differentparts of the image forming apparatus from those of the image formingapparatus 1 are intensively explained. Note that since the mainconfiguration of the image forming apparatus of the embodiment is commonwith the main configuration of the image forming apparatus 1 of thefirst embodiment shown in FIG. 1 other than the medium stacking device502, FIGS. 1, 2 will be referred if needed.

The extending part 555 of the sheet guide 520 is formed to have a widthforming a necessary minimum gap to guide and smoothly slide a side part555 b and a side part 555 a. The side part 555 b is guided by the guidewall 342 a formed in the medium stack plate 310 and the side part 555 ais guided by the guide wall 342 b formed in the medium stack plate 310.In the same manner, the extending part 556 of the sheet guide 520 isformed to have a width forming a necessary minimum gap to guide andsmoothly slide a side part 556 b and a side part 556 a. The side part556 b is guided by the guide wall 341 a formed in the medium stack plate310 and the side part 556 a is guided by the guide wall 341 b formed inthe medium stack plate 310.

Note that, here, the side parts 555 a, 555 b of the extending part 555and the side parts 556 a, 556 b of the extending part 556 correspond toan abutment part. The guide walls 341 a, 341 b, 342 a, and 342 bcorrespond to support parts.

In addition, the extending part 555 of the sheet guide 521 is formed tohave a width forming a necessary minimum gap to guide and smoothly slidea side part 555 b and a side part 555 a. The side part 555 b is guidedby the guide wall 342 a formed in the medium stack plate 310 and theside part 555 a is guided by the guide wall 343 b formed in the mediumstack plate 310. In the same manner, the extending part 556 of the sheetguide 521 is formed to have a width forming a necessary minimum gap toguide and smoothly slide a side part 556 b and a side part 556 a. Theside part 556 b is guided by the guide wall 344 a formed in the mediumstack plate 310 and the side part 556 a is guided by the guide wall 344b formed in the medium stack plate 310.

The flange 581 restricts detachment of the extending part 556 of thesheet guide 520 and the extending part 555 of the sheet guide 521 below(here, the minus side of Z axis. The flange 582 restricts detachment ofthe extending part 555 of the sheet guide 520 and the extending part 556of the sheet guide 521 below (here, the minus side of Z axis).Accordingly, the respective sheet guide 520 and the sheet guide 521herein individually move without linking each other.

Note that, here, the sheet guide 520 corresponds to a first movementpart. The sheet guide 521 corresponds to a second movement part. Thepair of extending parts 555, 556 of the sheet guide 520 corresponds to afirst movement restriction part. The pair of racks 555, 556 of the sheetguide 521 corresponds to a second movement restriction part. Therestriction surface 351 of the sheet guide 520 corresponds to a firstmedium restriction part. The restriction surface 351 of the sheet guide521 corresponds to a second medium restriction part.

In the above mentioned configuration, operation of the sheet guides 520,521 in the medium stacking device 502 will be explained.

Firstly, the medium stacking device 502 is pushed down against bias ofthe spring 309 by an operation device (not shown), so that the contactpart 311 of the medium stacking device 302 shown in FIG. 2 (hereinreferred to as 502) is separated only at a predetermined interval fromthe pickup roller 303, and the medium stacking device 502 is restrictedat the position where the medium stacking device 502 is pushed down. Inthe state where the medium stacking device 502 is pushed down in thisway, the recording sheets 370 are placed on the manual feed tray. Atthis time, the sheet guide 520 and the sheet guide 521 are moved tooutside and the recording sheets 370 are stacked on the medium stackingdevice 502 so that the width direction edges of the recording sheet 370are positioned on each of the stacking surfaces 352 a of the sheet guide520 and the sheet guide 521. Each of the restriction surfaces 351 of thesheet guides 520 and 521 are moved in a center direction until therestriction surfaces 351 abut on end surfaces of the recording sheets370.

At this time, since the sheet guide 520 and the sheet guide 521 do notlink each other, they need to be individually moved by a user.

After determination of a position of the width direction of therecording sheet 370 on the medium stacking device 502 is performed asmentioned above, position restriction by an operation device (not shown)is unlocked and as shown in FIG. 2, the top sheet of the stackedrecording sheets 370 contacts the pickup roller 303 by bias force of thespring 309. In such a state, the pickup roller 303 activates and therecording sheet 370 is fed, the recording sheet 370 is fed in thedirection of arrow A in FIG. 12.

At this time, in the case where skew generates in the recording sheet370 and a pressure force acts on the restriction surface 351, since afarthest side part of an extending part from a point of action of forcecontacts the guide wall of the medium stacking plate 310, skew can bereduced in comparison with the case where only one extending part havingsimilar dimension accuracy is used.

For example, in the case where the sheet leading side (direction ofarrow A side) of the restriction surface 351 of the sheet guide 520shown in FIG. 17 is pressed by a pressure force Fc1 due to skew of therecording sheet stacked on the medium stacking device 502, a front edge555 h of the side part 555 b of the extending part 555 contacts theguide wall 342 a (FIG. 16) of the medium stacking plate 310, thereby, anincline of the sheet guide 520 with respect to the direction of arrow Acan be restricted.

In the same manner, in the case where the sheet trailing side (oppositeside of direction of arrow A side) of the restriction surface 351 of thesheet guide 520 shown in FIG. 17 is pressed by a pressure force Fc2 dueto skew of the recording sheet stacked on the medium stacking device502, a front edge 556 h of the side part 556 a of the extending part 556contacts the guide wall 341 b (FIG. 16) of the medium stacking plate310, thereby, an incline of the sheet guide 520 with respect to thedirection of arrow A can be restricted. Such a mechanism of preventionof rotation of the sheet guide 521 disposed so as to face the sheetguide 520 is similar to the above mentioned mechanism.

As mentioned above, according to the medium stacking device of theembodiment, even if skew is generated in the carried recording sheet,thereby, since an incline of the sheet guides 520, 521 is suppressedwith respect to the sheet carrying direction (the direction of arrow A),and the skew of the recording sheet can be diminished. Furthermore,according to the explanation on FIG. 10 of the first embodimentmentioned above, respectively, one of the extending part 556 and theextending part 555 is disposed in the direction of arrow A side and theother is disposed in the opposite side of the direction of arrow A sidebased on the center in the direction of arrow A of the restrictionsurface 351. Thereby, the above mentioned effects of the embodiment canbe more efficiently obtained regardless of directions of skew.

Note, in the embodiment, the sheet guide to which the two extendingparts are provided is shown as an example. However, same effects can beobtained by a sheet guide having two or more extending parts.

Fourth Embodiment

FIG. 18 is an external perspective view illustrating a configuration ofa sheet guide 620 (621) in the fourth embodiment.

A medium stacking device employing the sheet guide 620 (621) has a maindifferent point from the image forming apparatus employing the abovementioned medium stacking device 502 of third embodiment shown in FIG.16. The point is that extending parts 655, 656 (555, 556 in the thirdembodiment) have a different shape from that of the extending parts 555,556. Accordingly, the same reference numbers are put to, and explanationand figures are omitted for parts of the image forming apparatusemploying these sheet guides 620 (621) that are common with the imageforming apparatus 1 of the first embodiment mentioned above (FIG. 1).Different parts of the image forming apparatus from those of the imageforming apparatus 1 are intensively explained. Note that since the mainconfiguration of the image forming apparatus of the embodiment is commonwith the main configuration of image forming apparatus 1 of the firstembodiment shown in FIG. 1 other than the medium stacking device, FIGS.1, 2 will be referred if needed. In this embodiment, the movementrestriction parts are realized with two restriction members (extendingparts 655 and 656). The number of the restriction members for onemovement restriction part is preferably two, but may be three or more.

A shape of the extending part 655, 656 of the sheet guide 620 (621)corresponds to a shape of the rack 355, 356 of the sheet guide 320 (321)shown in FIG. 7 explained in first embodiment other than the tooth parts355 d, 356 d. Accordingly, when this sheet guide 620 (621) is installedto the medium stacking plate 310, in FIG. 16 explained in the thirdembodiment, instead of the side parts 555 b, 556 b of respectiveextending parts 555, 556, like the bias parts 355 c, 355 e and the biasparts 365 c, 365 e in FIG. 4, the bias parts 655 c, 655 e of the sheetguide 620 face and press the guide wall 342 a; the bias parts 656 c, 656e of the sheet guide 620 face and press the guide wall 341 a; the biasparts 655 c, 655 e of the sheet guide 621 face and press the guide wall343 a; and the bias parts 656 c, 656 e of the sheet guide 621 face andpress the guide wall 344 a.

In the above mentioned configuration, since method of setting recordingsheets on the medium stacking device is identical to that of the abovementioned third embodiment, the explanation of the method will be hereinomitted.

When a set recording sheet is carried in the direction of arrow A, forexample, in a case where a sheet leading side (side of direction ofarrow A) of the restriction surface 351 of the sheet guide 621 shown inFIG. 18 is pressed by the pressure force Fc1 due to skew of therecording sheet stacked on the medium stacking device, since forces arerespectively led to a direction where the bias part 655 e presses theguide wall 342 a and the bias part 656 e presses the guide wall 341 a, arestrative force Fa4 generated from the bias part 655 e and a restrativeforce Fa2 generated from the bias part 656 e respectively resist theseforces. Thereby, an incline of the sheet guide 620 with respect to thedirection of arrow A can be restricted.

In the same manner, in a case where a sheet trailing side (opposite sideof direction of arrow A) of the restriction surface 351 of the sheetguide 620 shown in FIG. 18 is pressed by the pressure force Fc2 due toskew of the recording sheet stacked on the medium stacking device, sincethe front edge part 656 h of the side part 656 a of the extending part656 functions as a fulcrum, forces are respectively led to a directionwhere the bias part 655 c presses the guide wall 342 a and the bias part656 c presses the guide wall 341 a, a restrative force Fa3 generatedfrom the bias part 655 c and a restrative force Fa1 generated from thebias part 656 c respectively resist these forces. Thereby, an incline ofthe sheet guide 620 with respect to the direction of arrow A can berestricted. Such a mechanism of prevention of incline of the sheet guide621 disposed so as to face the sheet guide 620 is similar to the abovementioned mechanism.

As mentioned above, according to the medium stacking device of theembodiment, even if skew is generated in the carried recording sheet,thereby, since an incline of the sheet guide 620, 621 is suppressed withrespect to the sheet carrying direction (the direction of arrow A), andthe skew of the recording sheet can be diminished. Furthermore,according to the explanation on FIG. 10 of the first embodimentmentioned above, respectively, one of the extending part 656 and theextending part 655 is disposed in the direction of arrow A side and theother is disposed in the opposite side of the direction of arrow A sidebased on the center of the restriction surface 351 in the direction ofarrow A. Thereby, the above mentioned effects of the embodiment can bemore efficiently obtained regardless of directions of skew.

Note, in the embodiment, the sheet guide to which the two extendingparts are provided is shown as an example. However, same effects can beobtained by a sheet guide having two or more extending parts.

Through the specification, a pair of racks (355, 356), a pair ofextending parts (555, 556), and another pair of extending parts (655 and656) are disclosed as the restriction members for the movementrestriction parts. However, the restriction members are not necessarilyonly two components, but may be three or more components which functionto regulate the movement of the sheet guide.

In the above mentioned embodiments, applications of the presentinvention to an electrographic printer are explained. However, thepresent invention is not limited to the embodiments and may be appliedto a multifunction printer (MFP), a facsimile device, a photocopymachine, and the like. In addition, in the above mentioned embodiments,applications of the present invention to manual feed trays areexplained. However, the present invention may be applied to a cassettetray, an Auto Document Feeder (ADF), and the like.

1. A medium stacking device, comprising: a medium stacking part stackinga medium; and a first movement part movably provided with respect to themedium stacking part; wherein the first movement part has a first mediumrestriction part restricting a position of the medium, and a firstmovement restriction part including a plurality of restriction members,each of which engaging with the medium stacking part and restricting adirection of the movement of the first movement part.
 2. The mediumstacking device according to claim 1, wherein the restriction membersare provided substantially in parallel with respect to a medium carryingdirection, and the restriction members substantially vertically extendwith respect to the medium carrying direction.
 3. The medium stackingdevice according to claim 1, wherein each of the restriction membersincludes an abutment part, and the medium stacking part has a supportpart contacting the abutment part.
 4. The medium stacking deviceaccording to claim 3, wherein each of the restriction members has a biaspart for biasing the abutment part against the support part.
 5. Themedium stacking device according to claim 1, further comprising: a gearpart rotatably held by the medium stacking part, wherein one of therestriction members has a tooth part engaging with the gear part.
 6. Themedium stacking device according to claim 2, wherein the first movementrestriction part has two of the restriction members, and one of therestriction members is positioned at an upstream side along the mediumcarrying direction, the other of the restriction members is positionedat a downstream side along the medium carrying direction.
 7. The mediumstacking device according to claim 1, comprising: a second movement partdisposed so as to face the first movement part and movably provided withrespect to the medium stacking part, wherein the second movement parthas a second medium restriction part restricting the position of themedium, and a second movement restriction part including a plurality ofother restriction members, each of which engaging with the mediumstacking part and restricting a direction of the movement of the secondmovement part.
 8. The medium stacking device according to claim 7,wherein the restriction members of the first medium restriction part andthe restriction members of the second medium restriction part areprovided substantially in parallel each other, and the restrictionmembers of the first movement restriction part substantially verticallyextend with respect to the medium carrying direction and toward thesecond medium restrict part, the restriction members of the secondmovement restriction part substantially vertically extend with respectto the medium carrying direction and toward the first medium restrictionpart.
 9. The medium stacking device according to claim 8, wherein eachof the first movement restriction part and the second movementrestriction part includes an abutment part, and the medium stacking parthas two support parts, one support part contacting the abutment part ofthe first movement restriction part, the other support part contactingthe abutment part of the second movement restriction part.
 10. Themedium stacking device according to claim 9, wherein each of the firstmovement restriction part and the second movement restriction part has abias part for biasing one of the abutment parts into the correspondingsupport part .
 11. The medium stacking device according to claim 8,further comprising: a first gear part and a second gear part rotatablyheld by the medium stacking part and provided along the medium carryingdirection and at a substantially middle of the first and second mediumrestriction parts, wherein the restriction members of the first movementrestriction part respectively have a tooth part engaging with the firstgear part and another tooth part engaging with the second gear part, andthe restriction members of the second movement restriction partrespectively have a tooth part engaging with the first gear part andanother tooth part engaging with the second gear part.
 12. The mediumstacking device according to claim 7, wherein the first movement partand the second movement part have an identical shape.
 13. The mediumstacking device according to claim 8, further comprising: a transferringpart engaging with the first gear part and the second gear part andlinking the first gear part to the second gear part.
 14. An imageforming apparatus, comprising: the medium stacking part according toclaim 1.